A piperidyl group-containing polymer, especially a nitroxide radical-containing polymer is known to be stable under various conditions and used as a weatherability improver for resins, a stabilizer or an electrode material for secondary batteries, or the like. Nitroxide radical-containing polymers produced by radical polymerization are described in Polym. J., 14(5), 363 (1982) and Japanese Patent Laid-Open Publication No. 2002-313344, while a nitroxide radical-containing polymer produced by anionic polymerization is described in J. Polym. Sci., Polym. Chem. Ed., 10, 3295 (1972).
However, there have been problems that the radical polymerization had difficulty in controlling the molecular weight and its distribution and that in conventional anionic polymerization, the yield was low and high-molecular-weight polymers could not be obtained. Another problem was that, since these polymers had almost no conductivity in themselves, addition of a large amount of a conductive material was required when used as positive electrode materials for batteries.
Japanese Patent Laid-Open Publication No. 2001-210314 proposes adding a polymeric hindered amine, in which a hindered amine moiety is incorporated in a (meth)acrylic ester unit, to a positive electrode, a negative electrode, or a separator. For such (meth)acrylic ester-based polymer containing a hindered amine moiety, however, a low-molecular-weight polymer had high solubility to electrolytes whereas when powder of high-molecular-weight polymer was mixed with carbon to prepare a positive electrode material, the effect largely varied from material to material; therefore, both the cases were impractical.